FRESNO, Calif.  Automobile manufacturers sued Tuesday to block California regulators from adopting the world's toughest vehicle-emissions standards, arguing in a lawsuit that the standards are the federal government's responsibility.

"Federal law is designed to ensure a consistent fuel economy program across the country," Fred Webber, president and chief executive of the Alliance of Automobile Manufacturers, said in announcing the lawsuit, which had been expected since the regulations were adopted in September to reduce greenhouse gases.

The complaint was filed in federal court in Fresno, where previous similar challenges have been filed against the state's clean-air efforts, the most stringent in the nation.

Officials with the California Air Resources Board said they had not seen the details of the lawsuit Tuesday afternoon, and declined comment.

The regulations are scheduled to be phased in beginning in 2009. The California Air Resources Board estimates they would cut exhaust emissions in cars and light trucks by 25 percent and in larger trucks and SUVs by 18 percent.

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Seven other states have taken steps to emulate California's regulations -- New York, New Jersey, Connecticut, Massachusetts, Maine, Vermont and Rhode Island. Together with California, they represent one quarter of American car sales.

Under the new rules, these states would require automakers to use better air conditioners, more efficient transmissions and smaller engines.

The lawsuit contends that only the National Highway Traffic Safety Administration has the authority to set fuel economy standards.

But national advocacy groups protested the lawsuit, which they said was an attack on the right of states to protect their population from the effects of dirty air.

"That's what this suit is about -- air pollution, not fuel economy," said David Doniger, policy director for the Natural Resources Defense Council's Climate Center.

State regulators sidestepped the issue by regulating carbon dioxide emissions, not fuel economy. But the alliance argues that "carbon dioxide and fuel economy are synonymous," noting the U.S. Environmental Protection Agency uses carbon dioxide emissions to gauge the vehicles' fuel efficiency.

The alliance said complying with the California standards would increase the cost of a new vehicle by an average of $3,000. It also said the regulations would reduce consumer choices because manufacturers would likely dump vehicles with higher emissions, such as full-size pickups with large engines. Air regulators estimated the cost at about $1,000 per vehicle.